Mapping Stability/Storage (was Re: M-Label or MVALID, and dangers with mappings?)

Mark Davis mark at
Sun Apr 12 03:13:34 CEST 2009

(1) A browser captures a URL from an address bar, and sends it to a backend
program, as is. The second process examines it for spoofing issues, and
communicates back to the first. Remapping loses information that might be
relevant to the user.
(2) I include http://Ö in this email message. My emailer is IDNA aware,
and recognizes this as a URL. I send the email to yours, which is, I
presume, also IDNA aware. I don't want either one to lowercase it.


The question to back to you is what concrete problems are solved by making
this a MUST.


2009/4/11 John C Klensin <klensin at>

> --On Saturday, April 11, 2009 08:57 -0700 Mark Davis
> <mark at> wrote:
> >...
> > I think what we can say is programs SHOULD convert to the
> > canonical U-Label form before transmitting to other IDNA-aware
> > programs, and to the A-Label form before transmitting to
> > non-IDNA-aware programs. (The above isn't formal language, but
> > you can see what I mean.)
> Can you identify the use cases for exceptions to this rule
> (i.e., what justifies a SHOULD, rather than a MUST) rather than
> making the non-conversion behavior non-conforming?
>   john
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